The present invention relates to a nickel-base single-crystal superalloy applied to high temperature parts (heat resisting parts) of an industrial gas turbine, such as turbine blades and vanes, a method of manufacturing such superalloy, and gas turbine high temperature parts made of such a superalloy or manufactured in accordance with such method.
With a trend towards high efficiency of a gas turbine, combustion temperature therein rises, so that material for turbine rotor and stator blades has changed from a type of conventional cast alloy to a type of directionally solidified alloy, in which a crystal grain boundary along a stress axial direction is removed to improve creep strength at high temperatures and further to a type of single-crystal alloy, in which grain boundary strengthening elements, the presence of which is a cause for decreasing heat treatment window, are excluded by allowing the crystal grain boundary itself to disappear, so that an optimum heat treatment is applied to increase a volume fraction of gamma prime phase, whereby the creep strength at the high temperatures are further improved.
Development of the single-crystal alloy has switched from the first generation single-crystal superalloy to the second and third generation single-crystal superalloys, aiming at a still further improvement in the creep strength.
The first generation single-crystal superalloy contains no rhenium. Examples of such an alloy include xe2x80x9cCMSX-2xe2x80x9d disclosed in Japanese Laid-Open Patent Publication No. SHO 59-19032, xe2x80x9cRenexe2x80x2N4xe2x80x9d disclosed in U.S. Pat. No. 5,399,313, xe2x80x9cPWA-1480xe2x80x9d disclosed in Japanese Laid-Open Patent Publication No. SHO 53-146223, and the like.
Stress rupture temperature of the second generation single-crystal superalloys contain about 3% of rhenium is increased by about 30xc2x0 C. in comparison with that of the first generation single-crystal superalloys. Examples of such an alloy include xe2x80x9cCMSX-4xe2x80x9d disclosed in U.S. Pat. No. 4,643,782, xe2x80x9cPWA-1484xe2x80x9d disclosed in U.S. Pat. No. 4,719,080, xe2x80x9cRenexe2x80x2N5xe2x80x9d disclosed in Japanese Patent Laid-Open Publication No. HEI 5-59474, and the like.
The third generation single-crystal superalloy contains about 5% to 6% of rhenium. Examples of such an alloy include xe2x80x9cCMSX-10xe2x80x9d disclosed in Japanese Patent Laid-Open Publication No. HEI 7-138683, and the like.
These single-crystal alloys have been remarkably developed mainly in a field of aircraft jet engines and small gas turbines. It has been intended to convert such technology into a field of large-sized gas turbines for industrial use because of achieving high temperatures directing to improvements in combustion efficiency.
The large-sized gas turbine for industrial use takes longer time for design life as compared with aircraft jet engine or small gas turbine. Accordingly, blade materials require characteristic properties to inhibit formation of TCP (Topologically Close-Packed phase), which serves as a deteriorating phase when used, i.e., a good structural stability.
In the third generation single-crystal superalloy, addition of rhenium in an amount of 5% to 6% makes it possible to increase creep strength in comparison with the second generation single-crystal superalloy. However, the TCP phase, which may serve as a initiation site of creep and low-cycle fatigue failure, tends to occur after using a long period of service time. In the light of such problems, it is therefore hard to apply the third generation single-crystal superalloy to material for the large-sized gas turbine. In view of increase in firing temperature, there has however been demanded material having further higher creep strength.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a nickel-base single-crystal superalloy improved in creep strength and microstructural stability under a high temperature condition, a method of manufacturing such a superalloy and gas turbine high temperature (heat resisting) parts made thereof.
After studies of components of elements contained in a superalloy and amounts thereof, the inventors of the subject application had a finding that there can be obtained a single-crystal alloy, which has at least the same creep strength as that of a single-crystal alloy of the second generation at a temperature of up to 900xc2x0 C. and under a stress of at least 200 MPa, and on the one hand, the creep strength larger than that of the above-mentioned single-crystal alloy of the second generation at a temperature of at least 900xc2x0 C. and under a stress of up to 200 MPa, in addition to an excellent structural stability, a method for manufacturing such a specific superalloy and a high temperature (hest resisting) gas turbine part made thereof.
That is, the above and other objects can be achieved according to the present invention by providing, in one aspect, a nickel-base single-crystal superalloy, essentially consisting of, in percentages by weight, 4.0% to 11.0% of cobalt, 3.5% to less than 5.0% of chromium, 0.5% to 3.0% of molybdenum, 7.0% to 10.0% of tungsten, 4.5% to 6.0% of aluminum, 0.1% to 2.0% of titanium, 5.0% to 8.0% of tantalum, 1.0% to 3.0% of rhenium, 0.01% to 0.5% of hafnium, 0.01% to 0.1% of silicon, and a balance being nickel and inevitable impurity, a total amount of rhenium and chromium being not less than 4.0% and a total amount of rhenium, molybdenum, tungsten and chromium being not more than 18.0%.
Further, it is to be noted that an expression such as xe2x80x9c4.0% to 11.0% of cobaltxe2x80x9d in the present specification equivalently means xe2x80x9ccobalt of not less than 4.0% and not more than 11.0%xe2x80x9d, and this is to be applied throughout the present specification.
In another aspect, there is provided a nickel-base single-crystal superalloy, essentially consisting of, in percentages by weight, 5.0% to 10.0% of cobalt, 4.0% to less than 5.0% of chromium, 1.0% to 2.5% of molybdenum, 8.0% to 9.0% of tungsten, 5.0% to 5.5% of aluminum, 0.1% to 1.0% of titanium, 6.0% to 7.0% of tantalum, 2.0% to 3.0% of rhenium, 0.01% to 0.5% of hafnium, 0.01% to 0.1% of silicon, and a balance being nickel and inevitable impurity, a total amount of rhenium and chromium being not less than 4.0% and a total amount of rhenium, molybdenum, tungsten and chromium being not more than 18.0%.
In a further aspect, there is also provided a nickel-base single-crystal superalloy, essentially consisting of, in percentages by weight, 5.0% to 10.0% of cobalt, 4.0% to less than 5.0% of chromium, 1.0% to 2.5% of molybdenum, 8.0% to 9.0% of tungsten, 5.0% to 5.5% of aluminum, 0.8% to 1.5% of titanium, 5.0% to less than 6.0% of tantalum, 2.0% to 3.0% of rhenium, 0.01% to 0.5% of hafnium, 0.01% to 0.1% of silicon, and a balance being nickel and inevitable impurity, a total amount of rhenium and chromium being not less than 4.0% and a total amount of rhenium, molybdenum, tungsten and chromium being not more than 18.0%.
In a still further aspect, there is also provided a nickel-base single-crystal superalloy, essentially consisting of, in percentages by weight, all of elements listed in a following group A, at least one of elements selected from a following group B and a balance being nickel and inevitable impurity:
A: 4.0% to 11.0% of cobalt, 3.5% to less than 5.0% of chromium, 0.5% to 3.0% of molybdenum, 7.0% to 10.0% of tungsten, 4.5% to 6.0% of aluminum, 0.1% to 2.0% of titanium, 5.0% to 8.0% of tantalum, 1.0% to 3.0% of rhenium, 0.01% to 0.5% of hafnium, and 0.01% to 0.1% silicon,
B: less than 2% of niobium, less than 1% of vanadium, less than 2% of ruthenium, less than 1% of carbon, less than 0.05% of boron, less than 0.1% of zirconium, less than 0.1% of yttrium, less than 0.1 of lanthanum, and less than 0.1% of cerium.
In a still further aspect, there is also provided a nickel-base single-crystal superalloy, essentially consisting of, in percentages by weight, all of elements listed in a following group C, at least one of elements selected from a following group D and a balance being nickel and inevitable impurity:
C: 5.0% to 10.0% of cobalt, 4.0% to less than 5.0% of chromium, 1.0% to 2.5% of molybdenum, 8.0% to 9.0% of tungsten, 5.0% to 5.5% of aluminum, 0.1% to 1.0% of titanium, 6.0% to 7.0% of tantalum, 2.0% to 3.0% of rhenium, 0.01% to 0.2% of hafnium, and 0.01% to 0.1% silicon,
D: less than 2% of niobium, less than 1% of vanadium, less than 2% of ruthenium, less than 1% of carbon, less than 0.05% of boron, less than 0.1% of zirconium, less than 0.1% of yttrium, less than 0.1% of lanthanum, and less than 0.1% of cerium.
Hereunder, description will be given to advantageous effects of each element in the compositions of alloy as well as reasons for restricting the compositions.
Cobalt (Co) is an element which replaces nickel (Ni) in gamma-phase to strengthen the matrix in solid solution. The reason for limiting the cobalt content within the range of from 4.0% to 11.0% in percentages by weight in the present invention is in that with a cobalt content of less than 4%, a sufficient effect of strengthening the matrix in solid solution cannot be obtained, on the one hand, and with a cobalt content of over 11.0%, an amount of gamma prime phase decreases, degrading conversely the creep strength. A more preferable cobalt content is within the range of from 5.0% to 10.0%.
Chromium (Cr) is an element for improving high-temperature corrosion resistance. The reason for limiting the chromium content to at least (i.e., not less than) 3.5% in the present invention is in that, with a chromium content of under 3.5%, a desirable high-temperature corrosion resistance cannot be ensured. In the present invention, at least 0.5% molybdenum, at least 7.0% tungsten and at least 1.0% rhenium are contained as described later in order to improve the high-temperature strength. Chromium, molybdenum, tungsten and rhenium mainly enter into the gamma-phase in solid solution. When the amounts of them in the solid solution exceeds the prescribed limitations, the TCP such as rhenium-chromium-tungsten, rhenium-tungsten and the like precipitates in the nickel matrix. The TCP phase degrades a creep property and a low-cycle fatigue property. The higher limit of the chromium content by which the TCP phase does not precipitates, depends on an amount of gamma prime phase precipitated, which is a compound of aluminum, titanium, tantalum and nickel, as well as amounts of elements entering into the nickel matrix for solid solute strengthener. In accordance with the alloy composition of the present invention, the above-mentioned higher limit of the chromium content is under 5% so that the volume fraction (i.e., area ratio) of the TCP precipitates has no influence on the creep property and the low-cycle fatigue property as long as the total amount of rhenium, molybdenum, tungsten and chromium is up to (i.e., not more than) 18.0%.
In order to maintain a prescribed high temperature corrosion resistance, there has conventionally and generally been used material for stator blades of the industrial gas turbine, which has the chromium content of at least 10.0%, such as xe2x80x9cIN738LCxe2x80x9d having the chromium content of 16.0%, xe2x80x9cIN792xe2x80x9d having the chromium content of 12.4%. In the present invention, however, a successful result of the same high temperature corrosion resistance as that of the conventional material can be obtained by limiting the total amount of chromium and rhenium to at least 4%, not withstanding that the chromium content is within a low range of from 3.5% to less than 5%.
Molybdenum (Mo) is an element not only solid-solution strengthener of the gamma-phase, but also for making a gamma-gamma prime lattice misfit (xcex3/xcex3xe2x80x2) negative to accelerate the formation of raft structure, which is one of a strengthening mechanism at high temperatures. In the present invention, a molybdenum content is limited to at least 0.5%. It is necessary to contain at least 2% of molybdenum for obtaining required creep strength. With a molybdenum content of over 3.0%, an amount of molybdenum entering into the nickel matrix in solid solution exceeds the prescribed limitation so that the TCP such as xcex1-molybdenum, rhenium-molybdenum and the like precipitates. The upper limit of the molybdenum content is therefore limited to 3.0% (not more than 3.0%). It is more preferable to limit the molybdenum content within the range of from 1.0% to 2.5%.
Tungsten (W) is an element of solid-solute strengthener of the gamma-phase. In the present invention, a tungsten content is limited to at least 7.0%. The reason for such limitation is that at least 7.0% of tungsten is necessary for obtaining required creep strength. With a tungsten content of over 10.0%, the TCP precipitates such as xcex1-tungsten and chromium-rhenium-tungsten precipitates, degrading the creep strength. The upper limit of the tungsten content is therefore limited to 10.0%. A more preferable tungsten content is within the range of from 8.0% to 9.0%.
Aluminum (Al) is an element for forming gamma prime phase, which is a major strengthening factor of a nickel-base precipitation hardening superalloy and which is also an element forming an aluminum oxide on the surface of the alloy to contribute to improvements in oxidation resistance. In the present invention, the aluminum content of at least 4.5% is required to obtain a required creep characteristic property and a required oxidation resistance. With an aluminum content of over 6%, the range of heat treatment temperature for solid solution treatment is made narrowed, deteriorating the heat treatment properties. The aluminum content is therefore limited within the range of from 4.5% to 6.0%. A more preferable aluminum content is within the range of from 5.0% to 5.5%.
Titanium (Ti) is an element which is replaced by aluminum in the gamma prime phase to form Ni3 (Al, Ti), thereby serving as solid-solute strengthener of the gamma prime phase. In the present invention, the reason for defining that a titanium content is within the range of from 0.1% to 2.0% is that an excessive addition of titanium facilitates production of eutectic gamma prime phase or deposition of Ni3Ti-phase (xcex7-phase) and titanium nitride, hence deteriorating a creep strength. A more preferable titanium content is within the range of from 0.1% to 1%.
Tantalum (Ta) is an element which enters mainly into the gamma prime phase in solid solution to strengthen the gamma prime phase and contributes to oxidation resistance. An amount of at least 5.0% of tantalum is required to obtain the prescribed creep strength in the present invention. Addition of tantalum in an amount of over 8.0% facilitates production of eutectic gamma prime phase, resulting in a narrowed range of temperature at which a heat treatment process can be carried out in the solution heat treatment. The tantalum content is therefore limited within the range of from 5.0% to 8.0%. Further, in the present invention, control of the contents of gamma prime phase generation elements such as titanium, tantalum and the like, and the contents of gamma prime phase-strengthening elements in solid solution, such as chromium, molybdenum, tungsten, rhenium and the like facilitates growth of raft structure having a stress axis to which gamma prime of precipitation particles connects perpendicularly when stress such as creep is applied, thus improving a creep property in comparison with the conventional alloy. The formation of raft structure is under the influence of a gamma-gamma prime lattice misfit, which is a difference in lattice size between the gamma prime phase and the gamma-phase. In the present invention, adjustment of contents of aluminum, tantalum and titanium, which are the gamma prime phase generation elements, controls the lattice misfit. In a case where the titanium content is within the range of from 0.1% to 1.0%, the tantalum content is preferably within the range of from 6.0% to 7.0%. In a case where the titanium content is within the range of 0.8% to 1.5%, the tantalum content is preferably within the range of from 5.0% to less than 6.0%.
Rhenium (Re) is an element for strengthening the gamma-phase in solid solution and for improving high-temperature corrosion resistance. The reasons for the limitations of the rhenium content of from 1.0% to 3.0% will be described hereunder. An amount of at least 1.0% of rhenium is required to obtain the prescribed creep strength in the present invention. Addition of rhenium of over 3.0%, TCP phase, such as rhenium-molybdenum, rhenium-tungsten, rhenium-chromium-tungsten and the like will be precipitated. More preferable range of the rhenium content is within the range of from 2.0% to 3.0%.
Hafnium (Hf) is an element for improving the grain boundary strength. When a defect such as equiaxed grain, bigrains, high/low angle grain boundary and freckle are formed at the time of casting and subsequent heat treatment of the single-crystal turbine blade and vane, Hafnium strengthen the grain boundary between the defects and matrix. In the present invention, the hafnium content is limited within the range of from 0.01% to 0.5%. Addition of hafnium in an amount of over 0.5% decreases the melting point of a resultant alloy, deteriorating heat treatment characteristics thereof. Addition of hafnium in an amount of less than 0.01% cannot provide the above-described effects. In the present invention, the addition of hafnium in an amount of not more than 0.2% will be most preferable.
Silicon (Si) is an element to form an SiO2 oxide on the surface of the resultant alloy to serve as a protective oxide layer, thus improving oxidation resistance. In the conventional nickel-base single-crystal superalloy, silicon is considered as one of inevitable impurities. Silicon is however intentionally added in the present invention, utilizing silicon effectively in the improvement in oxidation resistance as mentioned above. It is conceivable that the oxide layer of SiO2, which does not easily tend to crack in comparison with the other protective oxide layer, has an effect of improving the creep and fatigue properties. Addition of silicon in an excessively large amount decreases the limitations by which the other elements enter in solid solution. The silicon content is therefore limited within the range of from 0.01% to 0.1. In the present invention, the addition of silicon in an amount of not more than 0.2% will be most preferable.
Niobium (Nb) is mainly dissolved in the gamma prime phase to strengthen the same. In the present invention, although such strengthening is performed mainly by tantalum, the niobium may be substituted therefor for achieving substantially the same functions. In comparison with a case where the tantalum is solely added, the case of adding the niobium as composite, the solution amount may be increased, providing an advantageous effect.
Vanadium (V) is dissolved in the gamma prime phase to strengthen the same. In a case, however, where vanadium is excessively added, the volume fraction of gamma-gamma prime eutectic is increased, and hence, a temperature range at which the heat treatment in the solution heat treatment can be done will be made narrowed.
Furthermore, according to the superalloy of the preferred embodiment of the present invention, the amounts to be added of the elements for forming the gamma prime phase such as titanium, tantalum or like and the elements for strengthening the gamma phase of chromium, molybdenum, tungsten, rhenium or like are adjusted so as to accelerate the formation of the raft structure. Raft structure is made by connecting gamma and gamma prime precipitate normal to a stress axis each other, and this structure seems to improve the creep property. The formation of raft structure has an influence on a gamma-gamma prime lattice misfit, which is a difference in size between the gamma prime phase of precipitation particles and the gamma-phase. In the present invention, the vanadium addition amount is limited to be less than 1.0% (weight) in consideration of the total addition of aluminum, tantalum, titanium and niobium.
Ruthenium (Ru) is an element to be dissolved in the gamma phase so as to strengthen the same. However, the ruthenium element has a high density and increase the specific gravity of alloy, and the addition thereof exceeds over 1.5%, the specific strength of the alloy is decreased. For this reason, the addition of ruthenium is limited to be less than 1.5%.
Carbon (C) is an element for improving the grain boundary strength. When a defect such as equiaxed grain, bigrains, high/low angle grain boundary, sliver and freckle are formed at the time of casting and subsequent heat treatment of the single-crystal turbine blade and vane, Carbon strengthen the grain boundary between the defects and matrix. When the carbon is added by more than 0.1%, a carbide is formed together with elements such as tungsten, tantalum or like contributing to the solid-solution strengthening, the creep strength is degraded and the melting point of the alloy is decreased, thus deteriorating the heat treatment characteristics. For this reason, in the present invention, the addition of the carbon is limited to be less than 0.1%.
Boron (B), as like as carbon (C) mentioned above, is an element for improving the grain boundary strength. When a defect such as equiaxed grain, bigrains, high/low angle grain boundary, sliver and freckle are formed at the time of casting and subsequent heat treatment of the single-crystal turbine blade and vane, Boron strengthen the grain boundary between the defects and matrix. When the boron is added by more than 0.05%, a boride is formed together with elements such as tungsten, tantalum or like contributing to the solid-solution strengthening, the creep strength is degraded and the melting point of the alloy is decreased, thus deteriorating the heat treatment characteristics. For this reason, in the present invention, the addition of the boron is limited to be less than 0.05%.
Zirconium (Zr) is, as like as boron (B) or carbon (C), is an element for improving the grain boundary strength. When a defect such as equiaxed grain, bigrains, high/low angle grain boundary, sliver and freckle are formed at the time of casting and subsequent heat treatment of the single-crystal turbine blade and vane, Zirconium strengthen the grain boundary between the defects and matrix. When the boron is added excessively, the creep strength will be decreased, and for this reason, the addition of the zirconium is limited to be less than 0.1%.
Yttrium (Y), Lanthanum (La) and Cerium (Ce) are elements for improving adhesive property of protective oxide layer, such as Al2O3, SiO2, Cr2O3 which were formed on the nickel-base superalloy. In a case where a gas turbine blade manufactured by using the nickel-base superalloy is utilized at non-coating state, the gas turbine blade is subjected to heat cycle due to start-and-stop operation. At such time, the protective oxide layer is likely to be spalled off in accordance with the difference in thermal expansion coefficients between the base metal and the protective oxide layer. However, the addition of the yttrium, lanthanum and cerium improve the adhesive property of the protective oxide layer. On the other hand, the excessive addition thereof will make the solubility of the other elements lower. Accordingly, it is determined that the addition of such yttrium, lanthanum and cerium are limited to be less than 0.1%, respectively.
The method for manufacturing the above-mentioned nickel base single-crystal superalloy comprises the steps of: preparing a nickel-base single-crystal superalloy element material having a chemical composition claimed in any one of the above aspects concerning the nickel-base single-crystal superalloy, from raw materials containing nickel, cobalt, chromium, molybdenum, tungsten, aluminum, titanium, tantalum, rhenium, hafnium and silicon; subjecting the superalloy element material to a solution heat treatment within a temperature range of from 1280xc2x0 C. to 1350xc2x0 C. under a condition of a vacuum or inert gas atmosphere; quenching the superalloy element material, which has been subjected to the solution heat treatment; subjecting the superalloy element material thus quenched to a first ageing treatment within a temperature range of from 1100xc2x0 C. to 1200xc2x0 C.; and then, subjecting the superalloy element material, which has been subjected to the first ageing treatment, to a second ageing treatment within a temperature range lower than that of the first ageing treatment, thereby obtaining the nickel base single-crystal superalloy.
A multi-step heat treatment or a single-step heat treatment may be carried out, at a temperature which is lower than that of the solution heat treatment by 20xc2x0 C. to 40xc2x0 C., prior to the solution heat treatment. With the superalloy of the present invention, the addition in amount of rhenium having a low diffusion rate in the nickel alloy is suppressed to less than 3% to thereby obtain a sufficiently high creep strength even in the first stage preliminary solution heat treatment.
It is preferable to limit a period of time during which the solution heat treatment is carried out up to 10 hours.
Hereunder, description will be given to the influence of the manufacturing process on the alloy properties of the nickel-base single-crystal superalloy.
According to the present invention, the precipitation of the gamma prime phase mainly in the nickel matrix strengthens the alloy. More specifically, in a case where the gamma prime phase is uniformly precipitated in the nickel matrix with the cuboidal form and a size of this precipitate is within the range of from about 0.2 xcexcm to 0.6 xcexcm, the highest high-temperature creep strength can be provided. In order to improve the creep strength at a high temperature, it is necessary to subject the alloy to the solution heat treatment to cause the gamma prime phase having a non-uniform shape, which has been precipitated during the casting process, to enter once into the nickel matrix in a solid solution and then to reprecipitate the gamma prime phase in a desired shape and size.
In view of this fact, the alloy is subjected to the solution heat treatment in which the alloy is heated to a temperature exceeding a melting temperature of the gamma prime phase to cause the gamma prime phase into the nickel matrix in the solid solution. The solution heat treatment, which is carried out at the temperature immediately below the melting temperature of the gamma phase, actually causes the gamma phase into the nickel matrix in the solid solution and reduces the period of time required for making the structure uniform, thus providing industrially useful effects.
On the other hand, mechanical strain is induced when machining the nickel-base single-crystal superalloy into turbine rotor and stator blades, applying a machine work to portions into which the blades are to be embedded and carrying out a blast working to clean the surfaces of the blades upon a coating process. The mechanical strain generated in the blast machining causes recrystallization to occur in the high-temperature treatment, degrading the creep strength. In view of this fact, it is preferable to carry out the solution heat treatment at the highest temperature by which no recrystallization occurs. However, a degree of mechanical strain introduced may vary in a prescribed range and the temperature by which recrystallization occurs may also vary. In addition, the alloy according to the present invention is locally melted at a temperature of at least 1350xc2x0 C. The temperature range for the solution heat treatment is therefore limited within the range of from 1280xc2x0 C. to 1350xc2x0 C.
In usual, the first ageing treatment functions also as diffusion heat treatment of coating. The temperature for the first ageing treatment is therefore limited within the range of from 1100xc2x0 C. to 1200xc2x0 C. in the present invention, taking into consideration the coating applicability. A more preferable temperature for the first ageing treatment is 1150xc2x0 C.
In addition, application of the multi-step heat treatment in different temperatures during the solution heat treatment permits to carry out the solution heat treatment at an increased high temperature without occurrence of partial melting. It is therefore possible to make the alloy microstructure uniform and precipitate the gamma prime phase having a rectangular shape and a uniform size. As a result, there can be obtained the nickel-base single-crystal superalloy having an excellent creep strength.
The content of rhenium having a low diffusion rate in the nickel alloy is limited up to 3% in the present invention. It is therefore possible to provide a remarkably high creep property even when the single step heat treatment is carried out.
It is preferable to carry out the solution heat treatment for a long period of time to diffuse the added elements, in order to make the alloy structure of the nickel-base single-crystal superalloy uniform. The extended period of time for the heat treatment leads to an increased cost. It is possible to obtain a uniform structure by carrying out the heat treatment within 10 hours in the solution heat treatment in a temperature range from 1280xc2x0 C. to 1350xc2x0 C., due to the fact that the content of rhenium having a low diffusion rate in the nickel alloy is limited up to 3% in the present invention.
In addition, it is preferable to make high temperature (heat resisting) gas turbine parts of the nickel-base single-crystal superalloy of the present invention having the above-described composition.
It is also preferable to make a high temperature (heat resisting) gas turbine part of the nickel-base single-crystal superalloy, which has been manufactured in accordance with the above-described method of the present invention for manufacturing such a superalloy.
It is to be noted that the nature and further characteristic features of the present invention will be made more clear from the following descriptions made with references of preferred embodiments and accompanying drawings.